Misceleanous > Misceleanous
LiPo battery packs in parallel
Ron:
Being of an inquisitive nature, and having a couple of LiPo battery packs that I'd like to parallel up to give improved flight times, I was wondering - idly to myself, the way you do, what conditions may apply to the charge state when you connect them.
If one is (say) half charged, and the other is fully charged, does the full one try to dump loads of current into the half charged one?
Various sources on the web say you can parallel up series packs, so you could have - 3S 20C 2P - but that is in one already made up 'pack'.
So presumably all cells would be charged and discharged together.
But can you parallel up separate packs?
Sounds a bit dodgy to me.
Ron
Happy Days:
Hi Ron
The answer is Yes,……….what was the question? :shock: (I’m sure some TV ad used to have that as it’s punch line. Didn‘t it? :lol: )
I have a powered plane that uses two sets of batteries in parallel. The system has worked fine for the past 3 years.
As to your question about one “half charged” pack being “charged” by another pack with a higher voltage on it, I’m not too sure. :?
Logic would suggest that it would, all be it at a very slow rate as the different potential between the cells only amounts to a very small percentage of their overall voltage.
However, I have a little thought that’s pricking the back of my mind :twisted: and telling me that Ohms Law stops one cell of the same type from charging up another. But having just written it down on paper I can’t see why one battery shouldn’t charge up another. :(
HHHmmmmmmm Worthy of further thought Ron. :?:
Keith
Happy Days:
Hang on a minute,………..The higher charged battery can’t charge the lower battery because there is infinite resistance between the battery contacts. i.e. there’s no circuit!
If you connect the positive and negative sides of the “pack” into a circuit load all the cells will start discharging, all be it at different rates depending on their internal resistance > state of charge. (Ignoring changes in internal resistance that occure through ageing and other minor matters.)
Well, I think that's right............. :roll:
Having thought some more on this matter, I've decided that the above is not valid.
I think the cells don't charge eachother because the potental difference is too low between the cells to over come the resistance of the connecting wires.
So endeth the lesson! :P
Ron:
--- Quote ---The answer is Yes,……….what was the question? :shock:
--- End quote ---
Ah I like that answer.
I think the question was 42.
No that's the answer to another question...
--- Quote ---As to your question about one “half charged” pack being “charged” by another pack with a higher voltage on it, I’m not too sure. :?
Logic would suggest that it would, all be it at a very slow rate as the different potential between the cells only amounts to a very small percentage of their overall voltage.
--- End quote ---
I guess this is the real answer.
With LiPo especially the voltage varies so little.
--- Quote ---However, I have a little thought that’s pricking the back of my mind :twisted: and telling me that Ohms Law stops one cell of the same type from charging up another. But having just written it down on paper I can’t see why one battery shouldn’t charge up another. :(
--- End quote ---
That's the thing. It seems like there would be nothing to stop it happening, but somehow.....
--- Quote ---HHHmmmmmmm Worthy of further thought Ron. :?:
--- End quote ---
Oh no, not more thinking :cry:
My brain hurts :(
Ron
DaveMc:
Yes, you can connect 2 packs in paralell.
Make sure both packs are equal and are both fully charges to within 100 - 200 mV of each other.
Also make sure both packs are good and will discharge their full capacity.
It is easier to think of Voltage and Current in term of Water.
Imagine 2 buckets of water. Bucket 1 is full and Bucket 2 is 50% full. Now connect both of them with a pipe. What do you think will happen to the water level in the Full bucket?
The water levels will try to balance. Water from the full bucket flows to the half full bucket and both buckets will end up with the same water level.... ie 75% full each.
2 paralell packs of say 11.1V 2200mAh when connected in paralell will try to balance out any potential difference between them. Of course the above water analogy will not result in a fire :)
A weaker pack will result in a fairly massive current drain placed on the stronger pack.
Best case.... the good pack may get damaged and you will have 2 bad lipo packs.
Worst case... your model plane/car/house goes up in smoke. :)
Charge your packs seperately and look after them.
The harness you use to make the paralell connection must be able to handle the increased capacity of your new battery pack and therfor any potential increase in current draw.
God i hope the 6 pack i have just drank this evening has not caused me to advise you to do something which will cause a big bang!!! :)
D.
Navigation
[0] Message Index
[#] Next page
Go to full version